Aerobic anoxygenic phototrophs are widespread and active members of Greenland Ice Sheet microbiomes

Abstract The Greenland Ice Sheet (GrIS) hosts diverse microbial communities where glacier ice algae, snow algae, and cyanobacteria act as key primary producers across bare ice, snow, and cryoconite habitats, yet the ecological roles of associated heterotrophic prokaryotes remain poorly understood. Aerobic anoxygenic phototrophs (AAPs), known to couple light harvesting to heterotrophy and enter trophic relationships with algae in marine systems, suggesting they may represent an important but underexplored functional group in supraglacial ecosystems. Using genome-resolved analyses of supraglacial metagenomes and metatranscriptomes from Greenland, we recovered nine AAP metagenome-assembled genomes (MAGs) (4% of the 229 recovered MAGs) consistently enriched in bare ice and cryoconite communities, but nearly absent in snow. A meta-analysis of 2 451 public metagenomes supported this cryospheric habitat association. AAP_MAGs were disproportionally enriched in thiosulfate oxidation and bicarbonate-dependent carbon assimilation pathways relative to other MAGs. Iron and CO oxidation pathways were broadly distributed across the GrIS microbiome, including in AAPs, together suggesting adaptation strategies in supraglacial ecosystems. Genomic evidence for algal coupling via sulfoquinovose degradation was limited. Overall, we document that AAPs are active and widespread in weathering crust habitats, highlighting their potential contributions to biogeochemical cycling in supraglacial ecosystems.